Much of the epic progress during the industrial revolution in the United States during the 19th and 20th century was powered by steam. However, the thermal efficiency of steam powered piston engines could not match that of the Otto or Diesel engines developed at the end of the 19th century. A substantial improvement in steam engine efficiency was however made when the uniflow steam engine was developed by Professor Stumpf in Germany and improved further in the U.S. by C. C. Williams high compression uniflow engine based on compression as described in U.S. Pat. Nos. 2,402,699 and 2,943,608 in which steam is compressed to boiler pressure by the piston return stroke thereby raising the steam temperature for example 95 to 342 degrees hotter than feed steam in a sizeable clearance volume that may be 7% to 14.5% of displacement. The thermal efficiency of even these engines while improved, could not however reach that of the internal combustion engine.
Recently, a substantial further advance has been made through the development of steam engines operating on a cycle that employs essentially zero clearance between the piston and the cylinder head at the end of the exhaust stroke while at the same time any steam in the cylinder is under little or no compression. This arrangement achieves a remarkable increase in thermal efficiency as disclosed in U.S. Pat. Nos. 8,448,440, 9,316,130, 8,661,817, 9,828,886 and U.S. patent application Ser. No. 15/794,486 filed Oct. 26, 2017, now U.S. Pat. No. 10,273,840 which are assigned to the Applicant's assignee and incorporated herein by reference. Engines in which both piston clearance and compression approach zero (the Z-Z operating principle) described in the latter five patents noted provide a thermal efficiency which ranges from an improvement of about 15% to an extraordinary 59% better than the best performing high compression uniflow engines that are widely recognized to have the highest thermal efficiency of any steam engine (see FIG. 1). The outstanding efficiency of the engines built according to the Z-Z patents listed above results from several factors including the Z-Z operating principle and benefits arising from the use of a unique, fast acting inlet valve which can open fully in some embodiments in less than 1 millisecond thereby avoiding losses formerly caused by a restriction in the flow of steam through the steam inlet valve while the valve is being opened by a cam or eccentric which may take as much as ⅓ to ½ of a crankshaft rotation resulting in reduced power output. By contrast, since the inlet valve of Z-Z engines of the present invention is opened fully almost instantly while the piston clearance is virtually zero, work output begins at the highest steam supply pressure earlier in the cycle thereby providing more power while also eliminating losses associated with having to compress to supply pressure a substantial quantity of steam that remains in the cylinder. One aim of the present invention is to be able to achieve these advantages disclosed in the Z-Z patents listed above while also timing the admission of steam into the cylinder electrically, e.g., by means of an electric engine control unit (ECU) over a wide range of cutoff settings without adversely affecting the advanced thermal efficiency of Z-Z engine principles.
In the Z-Z engine patents noted above and in other engines that use an electrically controlled steam cutoff, the magnetic field of an electromagnet typically acts on the valve itself. The valve must therefore be massive and formed from iron which can make operation at speeds over 5000 RPM difficult or impossible. Another obstacle is the delay caused by the time taken for the magnetic field of an electromagnet to build and then collapse resulting from the induction of a counter EMF which may take as long as 7-10 milliseconds or more. This limits the speed at which the engine can run especially if more than one valve function must be timed.
A more specific purpose of the present invention to retain the high efficiency and other advantages of the Z-Z engine patents noted above while actuating one or more valves by piston movement with little or no valve wear while opening or closing the valve in under 1 millisecond. By achieving these objectives in accordance with the present invention, valve size and weight can be minimized and a lighter weight non-ferrous valve such as a titanium valve can be used to facilitate oscillation at higher speeds. These advantages working together even make it possible in some embodiments to achieve a thermal efficiency exceeding that of a steam turbine in medium to small sizes, such as those under 1000 horsepower while also being lower in cost. The features and advantages noted above also make the invention well suited for applications such as electric power generation or the co-generation of heat and power, to power a vehicle or for use in solar power generation. A major advantage of the invention over internal combustion engines is its ability to use a variety of low grade fuels including waste or unrefined liquid fuels and low cost biomass without producing harmful nitrogen compounds or other air polluting emissions that are generated by internal combustion engines.
In view of the deficiencies of the prior art it is therefore one object to provide a way of actuating a steam inlet or exhaust valve by piston movement instead of a camshaft while timing at least one steam valve electrically as by means of an electric engine control unit (ECU) without the necessity of forming an inlet valve from a ferromagnetic material.
It is a more specific object to maintain the high thermal efficiency that characterizes the virtual zero or near zero clearance with zero or near zero pressure steam cycle of U.S. Pat. Nos. 8,448,440, 9,316,130, 9,828,886 and Ser. No. 15/794,486 wherein steam admission is controlled electrically through the action of a lightweight steam inlet valve that is able to reciprocate at over 50 cycles per second without the need of a cam shaft or eccentric.
Another object is to operate valves without the use of a camshaft or eccentric while controlling steam inlet valve cutoff timing electrically throughout a wide range as well as providing continuous variable electrical cutoff regulation under changing speeds and loads when needed to achieve a higher overall thermal efficiency than heretofore found in a reciprocating steam engine.
These and other more detailed and specific objects and advantages of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.